The present invention relates to an air conditioning apparatus for an automobile vehicle or the like and, more particularly, to an apparatus for controlling the temperature in a cabin of the automobile vehicle.
A typical prior art vehicle air conditioning apparatus comprises a duct and a blower for forcing air through the duct. An evaporator of a cooler and a core of a heater are disposed in the duct and are selectively utilized. A movable temperature control door such as an air mix door controls air flow through the evaporator and core and thereby the temperature of air flowing through the duct. The air mix door is positioned in accordance with sensed air temperature.
In connection with such a known vehicle air conditioning apparatus, it is frequently demanded to raise a low cabin temperature set up by a maximum cooling mode of operation of the air conditioner up to a given level higher than said low temperature, that is, to lower the cooling ability during the maximum cooling mode. The air conditioner meets this demand by progressively reducing the operating speed of the blower from a maximum speed predetermined for the maximum cooling mode while, at the same time, progressively opening the air mix door from its zero opening or full closed position in the maximum cooling mode. The result is an increase in the cabin or inside temperature from the low level to a higher level. Also demanded frequently is to lower the cabin temperature from a high level set up by a maximum heating mode to a lower level, meaning to reduce the heating ability in the maximum heating mode. The air conditioner in this case gradually decelerates the operation of the blower from a maximum speed predetermined for the maximum heating mode and, at the same time, varies the angular position of the air mix door from its full open position to progressively reduce the opening degree thereof. Then the high cabin temperature in the maximum heating mode will drop to a lower level.
Where the cabin temperature in the maximum cooling mode or the maximum heating mode is to be switched to another preset level without changing the operation mode, both of the blower and the air mix door start their actions simultaneously so that air once cooled by the cooler is again heated by the heater. This brings about drawbacks that a compressor driving the cooler is overloaded and that the temperature of air blown into the vehicle cabin undergoes an unpleasant sharp change. Meanwhile, the compressor associated with the cooler is usually turned off at a predetermined temperature level which is the freezing level of the cooler and, accordingly, the compressor is not turned off unless the cooler is cooled to a significantly low temperature. The compressor is therefore operated at a very high rate which overloads a rotary drive source for the compressor, i.e. the engine of the vehicle.
Thus, prior art air conditioning apparatuses for motor vehicles involve some critical problems still left unsolved.